This application relates to magnetic disc drives and more particularly to an apparatus for latching a disc drive actuator mechanism in a parked position when the drive is deenergized and unlatching the actuator mechanism when the drive is energized.
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modern disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (xe2x80x9cheadsxe2x80x9d) mounted to a radial actuator for movement of the heads relative to the discs. Each of the concentric tracks is generally divided into a plurality of separately addressable data sectors. The read/write transducer, e.g. a magnetoresistive read/write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment. Critical to both of these operations is the accurate locating of the head over the center of the desired track.
The heads are mounted via flexures at the ends of a plurality of actuator arms that project radially outward from the actuator body. The actuator body pivots about a shaft mounted to the disc drive housing at a position closely adjacent the outer extreme of the discs. The pivot shaft is parallel with the axis of rotation of the spindle motor and the discs, so that the heads move in a plane parallel with the surfaces of the discs.
Typically, such radial actuators employ a voice coil motor to position the heads with respect to the disc surfaces. The actuator voice coil motor includes a coil mounted on the side magnetic circuit comprising one or more permanent magnets and magnetically permeable pole pieces. When controlled direct current (DC) is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces. The actuator thus allows the head to move back and forth in an arcuate fashion between an inner radius and an outer radius of the discs.
When the drive is de-energized or shut down, the drive motor stops spinning and the actuator is rotated, for example counterclockwise, to position the heads at an inner radius landing zone location and xe2x80x9cparkxe2x80x9d or latch the actuator in this position. Often a magnetic latch is used to maintain the actuator in this position with the heads xe2x80x9cparkedxe2x80x9d in the landing zone. When a magnetic latch is used, an inadvertent external shock load, such as the drive being dropped, may cause sufficient rotational force to be applied to the actuator arms to overcome the magnetic attraction and thus the actuator arm may rotate from the landing zone to the data region of the discs without the discs spinning at all. This could destroy the stored data on the disc and could destroy the heads themselves. Consequently there is a need for a latch mechanism that ensures that the actuator stays in the park position any time that the disc drive motor is de-energized and, more importantly, when the discs are not spinning.
This de-energized latching at low disc spin rates has been traditionally accomplished by a wind operated latching mechanism which utilizes wind generated by the spinning discs while the drive motor is energized to push against a pivoting air filter member positioned adjacent the outer margin of the discs. This air filter member has a pivot portion, an air filter portion, and an elongated air vane which extends outward over the top disc in the disc stack. The air vane is pushed against by the air drawn along the surface of the disc. At the other end of the pivot portion latching mechanism is an elongated latch arm for engaging the actuator and a tab portion which carries a steel ball therein. The steel ball in the tab portion is positioned in the magnetic field generated by the VCM magnets and thus biases the latch counterclockwise such that the latch arm interferes with movement of the actuator arm off of the magnetic latch when the drive is de-energized and the actuator arm arrives at the park position with the coilform of the VCM against the magnetic latch.
The operation of this conventional latch mechanism is completely automatic, driven only by the VCM magnet magnetic field bias when the discs are stopped, and the force exerted by wind against the air filter and air vane in opposition to the magnetic field bias when the discs are spinning at normal speed. The size and placement of the steel ball on the tab portion are dictated by the requirement that the latch be disengaged when the discs are operating at full speed and engaged when the discs are turning at less than full operating speed with the actuator arm moved into the parked position.
The conventional air vane design has worked well for drives with three or four or more operating discs in the head disc assembly (HDA). However, in the case of drives designed for four discs and having only one or two discs installed, there have been cases where the air vane latch failed to move to the disengaged position when the drive was energized, thus preventing actuator movement and appearing to the user by the software as a disc crash or disc drive failure. In these cases, the failures appear to have occurred at high altitudes such as above 5,000 feet. Accordingly, there is a need for a magnetic wind operated latching apparatus for use in disc drives having only one or two discs which automatically disengages the actuator arm when the disc drive motor spins the discs at operating speed and engages the actuator arm when the disc or discs spin at less than operating speed and the actuator arm is in the parked position in a head disc assembly (HDA) designed to accommodate up to four or more discs.
Against this backdrop the present invention has been developed. The present invention is a modified top cover an HDA which has an air vane air filter latch apparatus therein having an air vane adapted to extend over the upper surface of a top disc on the disc drive motor. The top cover has a channel formed along an inside side wall surface adjacent the air filter portion of the air vane air filter latch apparatus. This arrangement directs and focuses the flow of wind generated by a disc rotating within the HDA against the air filter support bracket portion of the air vane air filter latch apparatus to provide an additional force, i.e., moment arm, on the pivoting air filter and latch that becomes important when only one or two discs are located on the drive motor in the HDA. This channel improves the opening speed of the air vane and its position causes a high pressure region directly in front of the air filter and air filter bracket. This effectively increases the pressure differential across the air filter bracket causing a higher torque to be applied to the latch apparatus, which results in a lower opening speed, thus providing an additional margin for positive operation of the latch when the disc is rotating at normal rotational speed. This channel potentially also permits a larger steel ball to be utilized in the latch apparatus thereby ensuring more positive latch and unlatch operations of the apparatus.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.